Are all bed sores preventable?

Thank you to everyone who has helped me so much in my grief journey. I am doing well ; moving forward with my family, job, life. Occasionally, I take time to still process things- more intellectually now than primarily emotionally. As you know Mom's last few weeks were in AL -receiving therapy 2x a day 6 days a week to build strength...until COVID hit and then she was diagnosed with autoimmune hepatitis and liver failure. The last 3 weeks before her passing, she grew very weak - could hardly eat, extreme nausea, intermittent diarrhea, edema, skin issues. She refused to go for tests ( she was tired, "done" with all the trauma, medical testing, hospitalizations over the last 5 years). She did not want to come home either, saying she needed too many more people to help her - much more care than I could provide at home. (I had cared for her at home mostly for the prior 5 years). The AL kept me updated, had wound doctors and a nurse treating her skin tears, etc. She had been dx. with cachexia/anorexia -tried meds - no real positive results regarding eating, etc. same with supplements ( prescription protein drinks, etc) and food I brought her that she liked ( this was during the pandemic).
My question is ... being frail, sick ( CHF, failing liver, stroke, etc. ) she was either in bed/or in wheelchair the last 2/3 weeks - standing during therapy, showers, etc. with 2 people assist.
Despite Roho cushions and mattress, as well as being repositioned periodically as tolerated, she developed 2 bedsores and a sore area on her back where her bones protruded ( she had severe osteoporosis as well). They were never infected, but were bandaged with medicine. I have always heard that ALL bedsores are preventable and are the result of poor hygiene/care and nutrition.
My Mom had developed one bedsore when I cared for her at home - but this was before her more progressive physical decline. It healed with medicine, bandaging, movement, etc. At the end stage of some one's life, when one is largely bedridden ( last 2/3 weeks), eating very little, and weak, are bedsores always preventable? I want to believe all the AL told me about what they were doing to care for her and help prevent them and care for her skin, move her, etc. but I am not sure if they should be believed...or in some very important ways, her care was sub-standard. I'd like to intellectually resolve this for myself to know if the AL and care was most likely remiss, or if with cachexia, decreasing ability to eat and increasing weakness, as well as her comorbidities, they were most likely unavoidable. Thanks for helping me resolve this.